Not so fast. Malware posing as antivirus software is spreading fast with tens of millions of computers (not Macs) infected each month, according to a report released from PandaLabs.

PandaLabs found 1,000 samples of fake antivirus software in the first quarter of 2008. In a year, that number had grown to 111,000. And in the second quarter of 2009, it reached 374,000, Luis Corrons, technical director of PandaLabs said in a recent interview.

The rogue antivirus software issues false warnings of infections in order to get people to pay for software they don't need. The programs also typically download a Trojan or other malware.

About 3 percent of the people who see the fake warnings fall for it, forking over $50 for an annual license or $80 for a lifetime license, according to Corrons.

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